This invention relates to an electronic component utilizing inductance (hereinafter collectively called an xe2x80x9cinductance componentxe2x80x9d), such as an inductor and a transformer used in a power supply for an electronic apparatus.
Year after year, there arises an increasing demand for an electronic component which is reduced in size and increased in power density. For an inductance component, various proposals have been made to meet the above-mentioned demand. For example, Japanese Unexamined Patent Publication No. S50-134173 (JP 50-134173 A) discloses an inductance component comprising a magnetic core and a permanent magnet attached thereto to apply a magnetic bias to the magnetic core so that the inductance is adjusted or controlled.
The inductance component includes two E-shaped magnetic cores faced to each other. The E-shaped magnetic cores have center magnetic legs faced to each other through the permanent magnet. To the center magnetic legs and the permanent magnet, a cylindrical excitation coil is fitted. Thus, the permanent magnet is arranged inside the cylindrical excitation coil. The permanent magnet generates a first magnetic field in a first direction while the excitation coil generates a second magnetic field in a second direction opposite to the first direction.
The inductance component in which the permanent magnet is arranged inside the cylindrical excitation coil is disadvantageous in the following respect. Upon occurrence of an abnormal current such as an inrush current rushing in or flowing through the excitation coil, the permanent magnet may possibly be demagnetized to become unable to exhibit the magnetic biasing effect, as will later be described in detail with reference to the drawing.
It is therefore an object of this invention to provide an inductance component in which demagnetization of a permanent magnet for applying a magnetic bias is suppressed.
It is another object of this invention to provide the above-mentioned inductance component small in size and high in power density.
Other objects of the present invention will become clear as the description proceeds.
According to this invention, there is provided an inductance component comprising a magnetic core forming a magnetic path, a cylindrical excitation coil fitted around a predetermined portion of the magnetic core, and a permanent magnet inserted into the magnetic path to apply a magnetic bias to the magnetic core, the permanent magnet being arranged outside the cylindrical excitation coil.